456 



MESOZOIC ERA— AGE OF REPTILES. 



there was in the region of the Connecticut Valley a shallow inland sea, 

 connected by a narrow outlet with the ocean. Into this the tides 



flowed and again 

 ebbed, leaving exten- 

 sive flats of mud or 

 sand ribbed with rip- 

 ple-marks. A pass- 

 ing shower pitted the 

 soft mud, and the 

 sun, coming out 

 again from the 

 breaking clouds, 

 dried and cracked 

 it. Huge bird-like 

 reptiles, and possibly 

 reptilian birds, saun- 

 tered near the shore- 

 margin in search of 



Fig. 721.— Portion of a Slab with Tracks of several Species of Bronto- food The tide Came 

 zoum (after Hitchcock). ' 



in again with its 

 freight of fine sediments, gently covered the tracks, and preserved them 

 forever. This occurred constantly for many ages about the end of the 

 Triassic or the beginning of the Jurassic period, for the tracks are 

 found near the middle of the series of strata. 



Richmond and North Carolina Coal-Fields. — The patches occurring 

 in Virginia and North Carolina are coal-bearing. They constitute the 

 Richmond and Piedmont coal-fields of Virginia, and the Deep River 

 and Dan River coal-fields of North Carolina. Fig. 722 gives a general- 



Fig. 722.— Section across Richmond Coal-field (after Daddow). 



ized section of the Richmond coal-fields taken from Daddow. The 

 strata of this field are sandstone and shales, 700 to 800 feet thick, lying 

 an irregular erosion-hollows of the gneiss. All the phenomena of a 

 coal-field are here repeated, viz., interstratified seams of coal and beds 

 of iron-ore, under-day 8 with roots, and roof -shales with leaf-impressions. 

 There are several seams of coal, the lowest of which is almost in con- 

 tact with the gneiss. Some of the seams are of great thickness — 

 thirty to forty feet — and the coal is very pure. It is probable that this 

 coal, like that of the Carboniferous times, was formed in a marsh, 

 which was sometimes converted into a lake. The plants found are 

 very decidedly Upper Triassic and Lower Jurassic, viz., Cycads, Coni- 



